Combat vehicles are at the present time equipped with passive suspension systems. Passive suspension systems consist of either mechanical or hydropneumatic springs in combination with fluid or friction dampers. The design of such systems is a compromise between the conflicting requirements for a stiff, heavily damped, suspension system to statically equilibrate and to dynamically stabilize the vehicle and a soft, lightly damped, suspension system which readily compresses and expands to isolate the vehicle hull from terrain disturbances. This compromise, results in a combat vehicle wherein the crew's ride, the weapon platforms' stability, the loss of contact with the ground, and the dampers' energy absorption, combine to limit the mobility, agility, and combat effectiveness of the weapon system as it travels cross-country. In addition, such compromise systems causes high forces to be transmitted between the ground and the vehicle so as to reduce the life of track, wheels, and bearings. Resultant shock and vibration may increase the maintenance requirements for associated sights, sensors, and electronics mounted interiorly of the vehicle's hull.
Numerous concepts for semi-active and active suspension systems whose object is to improve the ride and the stability of road and rail vehicles have been disclosed in United States Patents.
The semi-active suspension systems sense various operating conditions and control the damping force in accordance with the sensed conditions. U.S. Pat. No. 4,579,366, for example, describes a suspension apparatus of this type for use on road vehicles. In the '366 patent, the damping force of a hydropneumatic suspension is optimally controlled by controlling the opening of throttle valves disposed between hydropneumatic chambers and hydraulic actuators in accordance with the calculated road state on which a vehicle is riding. The suspension system of the '366 patent is not suited for harsh off-road operating conditions such as produced by large amplitude terrain disturbances encountered by combat vehicles. Such disturbances develop correspondingly large spring forces that cannot be compensated by optimization of damping forces alone.
The active suspension systems sense various operating conditions and control both the damping and the spring forces in accordance with the sensed conditions. The resultant performance of such systems requires input of considerable energy to drive pump components therein. U.S. Pat. No. 4,639,013 describes an active suspension apparatus of this type which attempts to reduce input energy requirements while improving ride. In the '013 patent, a single acting hydraulic actuator and an associated variable, offset, hydropneumatic chamber control the static component of the force acting on the vehicle and a parallel, double acting, hydraulic actuator and an associated servovalve and damping valve control the dynamic component of the force acting on the vehicle.
In a road vehicle, the dynamic component is primarily due to the acceleration, braking, and cornering inertial forces acting on the vehicle. These forces are smaller than the static force, and the aforedescribed parallel arrangement results in a substantial reduction in the energy required to stabilize the vehicle in reaction to these forces.
In an off-road vehicle, however, the dynamic component is primarily due to terrain disturbances producing large road wheel motions. The forces associated with these large motions are greater than the static force and the parallel arrangement results in an increase in the energy required to isolate the vehicle in reaction to these motions. Thus, the increased size, weight, and cost of the parallel arrangement is not offset by a comparable reduction in the energy requirements under off-road conditions and, therefore, this type of system is not applicable to off-road vehicles generally and to combat vehicles specifically.
U.S. Pat. No. 3,625,303 describes a proactive ride control system for combat vehicles. It requires a visual sensor to measure the terrain profile in front of the vehicle. The sensor inputs a computer which in turn regulates an active suspension to control the spring and damping forces. The sensor is used to anticipate the terrain in an attempt to increase the period of time to raise and lower wheels to reduce shock loading in the vehicle. Increased time also enables the input energy to the active system to be spread over time so as to reduce the power requirements and the size, weight, and cost of the suspension system components. In order to perform its intended purpose, the sensors must be reliable under rough operating conditions and must accurately determine terrain conditions. In practice neither objective is met. The present invention reduces energy requirements without use of such visual sensors.
U.S. Pat. No. 3,606,365 discloses an active suspension system for a wheeled vehicle such as a passenger train. The system has a piston connected to the car and a cylinder connected to the wheel (the connections can be reversed) for providing a leveling device between the car and the wheel. Fluid is directed into or is exhausted from the cylinder to change the relative distance between the wheel and the car in accordance with its acceleration or movement. The system has solenoid controlled valves which are opened and closed to selectively control the amount of fluid which is displaced relative to the piston to control the car wheel distance. The pressure fluid which is used to displace the piston is supplied from a reservoir connected to a pump. The pump raises the energy level of the fluid from atmosphere, the pressure fluid is held in the reservoir until a solenoid valve opens and then is directed into the cylinder to raise the car, e.g., to compensation for downward acceleration on opposition acceleration (upward car movement), the pressure fluid is directed through a dump valve to atmosphere to provide opposite compensation tending to lower the car back to level. Consequently, leveling fluid must continually be raised from a low energy state to a high energy state which is ten exhausted thereby to reduce the energy efficiency of the system. While such use of energy may be acceptable in certain wheeled vehicles such as passenger trains, it is unacceptable in systems in which fuel economy is critical such as in the case of combat vehicles whose battle field effectiveness depends in many cases on the range of the vehicle attributable to the on-board fuel capacity of the vehicle. In such cases an energy efficient suspension system can increase the vehicle's operating range by using a lesser amount of fuel for vehicle suspension control and a greater amount of on-board fuel to increase the operational range of the vehicle.